This invention relates generally to magnetic imaging and more particularly to an improved magnetographic imaging member and the method of its use.
There has recently been introduced a magnetic imaging system which employs a latent magnetic image in a magnetizable record surface. The latent image can be used for electronic transmission purposes or in a duplicating process.
In the duplicating process the image is developed with a magnetic toner. It is sometimes repetitively developed with transfer of the toner to a receiving surface taking place between each development.
Such a latent magnetic image is provided by any suitable magnetization procedure. Typically, a magnetizable layer of marking material is arranged in imagewise configuration on a magnetic substrate. Well known electrostatographic methods are sometimes used to arrange the magnetizable material in imagewise configuration. The imagewise configuration of magnetizable particles is converted to a magnetic latent image in the imaging surface by methods more fully described in U.S. Pat. Nos. 3,749,833 and 3,804,511 to Rait et al.
In one such method the magnetizable toner is developed in image configuration onto a xerographic recording surface. The toner is then magnetized by, for example, an electronic recording head. The layer supporting the magnetized toner is next brought into contact with a magnetizable layer, and the magnetized toner magnetizes the magnetizable layer in image configuration. A latent magnetic image is thus formed in the magnetizable layer corresponding to the imagewise arrangement of magnetized toner particles.
In another such method an imaging surface which is both magnetizable and xerographically imageable is used. Such an imaging surface comprises, for example, a mixture of iron oxide and zinc oxide supported on a substrate. A xerographic imaging is developed on the surface using magnetizable toner. The imaging surface and the magnetizable toner are then, sequentially, uniformly magnetized from the back with a recording head and uniformly erased from the front with a recording head. The magnetized toner particles act as a shunt for the erase head and prevent erasure of the magnetized surface in the developed image areas, thus forming a magnetic latent image.
Such surfaces which comprise a combination of magnetizable particles and photoconductive particles in a binder typically have low mechanical strength. A useful amount of magnetizable particles and photoconductive particles (generally about 30wt.% each) does not leave room for sufficient binder to form a strong layer.
It is also well known in the art to form a latent magnetic image by selective Curie point erasure of a premagnetized layer. Curie point erasure is accomplished by heating a premagnetized layer of magnetic material. When a magnetized material is heated past the Curie temperature it will lose its magnetism.
Curie point erasure of a unifomly magnetized hard magnetic material to achieve a latent magnetic image is typically accomplished by applying radiant heat through a mask. The magnetism in the material is erased by the heat except in the areas where the heat is prevented by the mask from heating the material.
The forming of a latent magnetic image by Curie point erasure has many advantages. It can be quickly accomplished, and the images so formed have high resolution and are desirable and convenient for use especially in duplicating systems where many copies are made from a single master.
Although good results are observed in the use of a latent magnetic image formed by the Curie point erasure system, there are certain disadvantages which are sought to be overcome. The use of a separate mask material to place over the magnetized material prior to heating is sometimes inconvenient. Such a separate mask requires close registration between the mask and the magnetic material during heating. The thickness of the separate mask does not contribute to high resolution because of the spacing between the mask image and the surface of the magnetic material, especially when the mask image is coated onto a transparent layer. The selection of a heat transmitting material to support the mask is known to present materials problems.
The commonly assigned copending applications Ser. No. 672,809 filed Apr. 1, 1976 now abandoned in favor of continuing application Ser. No. 726,853 filed Sept. 27, 1976. describe certain significant improvements over other Curie point erasure systems of the prior art. However, that system incorporates a spacing between the thermal radiation reflective mask and the conductive pre-magnetized layer.
A magnetic member which can be imaged by the Curie point erasure method without the use of a separate mask member is desirable. It is also desirable to provide a method of forming a latent magnetic image by Curie point erasure in which the mask is as close as possible to the magnetic layer so that resolution is improved. It is further desirable to provide a magnetographic imaging surface which can be imaged by the Curie point erasure method while avoiding the use of an image mask held on a separate heat transmitting layer.